This invention relates to a storage application and a storage system linked together to save a storage area in writing the same data.
As one of functions of the storage system, an automatic volume expansion technology has been disclosed (e.g., in JP 2003-15915 A). According to JP 2003-15915 A, in a volume pool constituted of a plurality of virtual volumes, no physical block is allocated to a block constituting a virtual volume immediately after creation of the virtual volume. When a use request (i.e., write I/O request or the like) is actually issued afterwards, a physical block is allocated from the volume pool to a target block of the use request. The automatic volume expansion technology makes it possible to reserve a sufficient size of the virtual volume, and to set a size of the volume pool to a proper size, and an administrator only needs to basically monitor the availability of the volume pool, avoiding virtual volume capacity expansion work. This technology is called allocation on use (AOU).
Such the virtual volume uses almost no capacity of a physical volume at the time of starting to use the volume. At the time of starting to use the volume, certain initialization processing is usually carried out by the storage application. For example, a file system executes file system creation processing (mkfs) as initialization processing. A logical volume manager executes volume group creation processing (vgcreate) as initialization processing. Through such the initialization processing, metadata indicating contents of volume construction information is written in the volume. Accordingly, the volume immediately after the initialization processing uses the capacity of the physical volume. In particular, the amount of volume construction information often depends on a volume size. Thus, a large-capacity volume consumes a certain amount of a physical volume capacity even while it is not really used.
JP 2005-11316 A discloses a technology of setting a volume allocation size immediately after initialization processing to be smaller than the volume allocation size during operation, in consideration of the fact that each writing size of the metadata is smaller than user data. With such the technology, it is possible to reduce a use capacity of the physical volume immediately after initialization.